ABSTRACT:

Surface area of methane hydrate in sediments is necessary to predict the amount of dissociated methane gas. It depends on the morphology how methane hydrate exists in sediments under the ground. The purpose of this study is to obtain a model equation for the surface area of methane hydrate in sediments as a function of porosity, hydrate saturation, and size of sediment particles. We conducted hydrate dissociation experiment in a pressure cell filled by glass beads. It is expected that the temperature in the cell first goes down to the equilibrium point due to hydrate dissociation, and that the dissociation ceases until heat is transferred from the surrounding cell walls. We simulated this process by using a numerical model with tentative surface areas. The surface area is, then, estimated by comparing the amounts of dissociated gas in the experiments and in the numerical simulations.

INTRODUCTION

The surface area of the methane hydrate existing in sediments is necessary to estimate the dissociation rate, together with the dissociation speed of methane hydrate. The latter was given in a function of molecular fraction of methane, temperature and pressure by part of the authors. The surface area depends on the morphology how methane hydrate exists in sediments under the ground. In this study, it is assumed that the area is a function of the size of sediment particles, porosity, and hydrate saturation. We first conducted hydrate dissociation experiment by using a pressure cell filled by glass beads. To control the porosity, we mixed the beads with a couple of diameters. Water was filled in the cell and hydrate was generated. The amount of the water determines the hydrate saturation. It is expected that the temperature in the experimental cell first goes down to the equilibrium point due to the hydrate dissociation.

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